The present invention relates to a beam splitting lens assembly especially suited for color electrostatic photography, facsimile reading and the like.
In an electrostatic copying machine to which the present lens assembly is particularly suited, a light image of an original document is split into three beam components of primary colors and radiated onto three respective charged photoconductive drums. Toner substances of colors complementary to said primary colors are applied to the drums to form toner images thereon. The toner images are sequentially transferred to a copy sheet in proper register to form a colored reproduction of the original document.
Such color electrostatic copying machines are, however, far from perfection. A problem which has remained heretofore unsolved is in the configuration of the optical system for imaging the three drums. Prior art optical systems generally comprise complicated and bulky arrangements of beam splitting mirrors and color filters which are expensive to produce on a commercial production basis and preclude reduction of size of the copying machine below a certain level. The various beam splitting mirrors and color filters have large surface areas and must be precision ground to provide freedom from distortion. They also absorb an undesirably large proportion of the light incident thereon. In addition, these elements are generally individually mounted which requires precision alignment. Such individually mounted elements are also sensitive to vibration which produces copies having images which are out of focus.